Efforts to clone the chitin synthetase gene from Saccharomyces cerevisiae have continued in collaboration with the laboratory of Dr. P. W. Robbins, at the Massachusetts Institute of Technology. A vector containing a fragment of yeast DNA was used to transform a chitin synthetase-deficient strain into an overproducer of the enzyme. Experiments are in progress to verify whether the DNA in question contains the structural gene for the synthetase. The beta(1 leads to 3)glucan synthetase of Neurospora crassa and Hansenula anomala has been dissociated into two components, one soluble and one insoluble, both of which are essential for activity, in addition to GTP or one of its analogs. Current evidence indicates that the soluble component contains a regulatory GTP-binding protein whereas the insoluble fraction would include the catalytic unit. A similar system appears to occur in S. cerevisiae. A new methodology for the localization of cell components attached to plasma membrane has been developed. In this procedure, the density of plasma membranes is modulated by attaching different amounts of concanavalin A to the surface of intact cells. The corresponding variation in the position of the membranes in a subsequent isopycnic gradient is recorded and compared with that of different markers. With this methodology, the association of most of the chitin synthetase with the yeast plasma membrane has been confirmed.